Transmission line terminator for signal integrity and EMI control

Abstract

A ferrite bead is placed in series with a terminating resistor on a transmission line such as a clock transmission line. In lower frequency ranges where the ferrite bead is substantially not effective, the transmission line will be effectively terminated by the resistor. In higher frequency ranges where the resistor is substantially no longer effective, the transmission line will be terminated by the ferrite bead. In one aspect, the resistor and ferrite bead are provided in a single surface mount package.

What is claimed is:  
     
       1. A source terminator device for a transmission line comprising: 
       a ferrite bead; and  
       a resistance in series with said ferrite bead  
       wherein said ferrite bead provides an impedance, above a knee frequency, greater than about a value of said resistance.  
     
     
       2. Apparatus as claimed in claim  1 , wherein said ferrite bead and said resistance are provided in a surface mount package. 
     
     
       3. Apparatus as claimed in claim  2 , wherein said surface mount package has a cross sectional footprint of less than about 5 mm 2 . 
     
     
       4. A source terminator device for a transmission line comprising: 
       a ferrite bead; and  
       a resistance in series with said ferrite bead;  
       wherein said resistance has a value of about 750 ohms.  
     
     
       5. A source terminator device for a transmission line comprising: 
       a ferrite bead; and  
       a resistance in series with said ferrite bead  
       wherein said resistance is integrally formed with said ferrite bead; and  
       wherein said resistance is formed by a method selected from providing a constriction in said ferrite bead or doping said ferrite bead.  
     
     
       6. An electronic device apparatus having at least a first circuit board, said first circuit board including a clock signal transmission line for transmitting clock signal between a clock driver and a load, comprising: 
       a transmission line terminator between said source and said transmission line, said terminator including a series-connected resistor and ferrite bead wherein said ferrite bead provides an impedance, above a knee frequency, greater than about a value of said resistance.  
     
     
       7. A transmission line terminator for source termination comprising: 
       resistance means electrically coupled between said source and said transmission line; and  
       ferrite bead means series-connected to said resistance means  
       wherein said resistance means has a value of about 750 Ohms.  
     
     
       8. A transmission line terminator for source termination comprising: 
       resistance means electrically coupled between said source and said transmission line;  
       ferrite bead means series-connected to said resistance means  
       wherein said ferrite bead means provides an impedance above a knee frequency, greater than about a value of said resistance means.  
     
     
       9. Apparatus as claimed in claim  8 , wherein said ferrite bead means and said resistance means are provided in a surface mount package. 
     
     
       10. Apparatus as claimed in claim  9 , wherein said surface mount package has a cross sectional footprint of less than about 5 mm 2 . 
     
     
       11. A transmission line terminator for source termination comprising: 
       resistance means electrically coupled between said source and said transmission line;  
       ferrite bead means series-connected to said resistance means  
       wherein said resistance means is integrally formed with said ferrite bead means; and  
       wherein said resistance means is formed by a method selected from providing a constriction in said ferrite bead or doping said ferrite bead.  
     
     
       12. An electronic device apparatus having at least a first circuit board, said first circuit board including a clock signal transmission line for transmitting clock signal between a clock driver and a load, comprising: 
       a transmission line terminator between said source and said transmission line, said terminator including series-connected resistance means and ferrite bead means wherein said ferrite bead means is a means for providing an impedance, above a knee frequency, greater than about a value of said resistance.  
     
     
       13. A method for source-terminating of a clock signal transmission line comprising: 
       forming a constriction in a ferrite bead for series-connecting a resistance and said ferrite bead to provide a line termination component;  
       electrically coupling said termination component between said source and said transmission line;  
       transmitting a sequential plurality of clock signals from said source, along said transmission line.  
     
     
       14. A method for source-terminating of a clock signal transmission line comprising: 
       series-connecting a resistance and a ferrite bead which provides an impedance above a knee frequency, greater than about a value of said resistance means to provide a line termination component;  
       electrically coupling said termination component between said source and said transmission line; and  
       transmitting a sequential plurality of clock signals from said source along said transmission line.  
     
     
       15. A method as claimed in claim  14 , further comprising providing said ferrite bead and said resistance in a surface mount package. 
     
     
       16. A method as claimed in claim  15 , wherein said surface mount package has a cross sectional footprint of less than about 5 mm 2 . 
     
     
       17. A method as claimed in claim  13 , further comprising integrally forming said resistance with said ferrite bead. 
     
     
       18. A method, as claimed in claim  14  wherein said impedance above a knee frequency is between about 200 ohms and 1000 ohms. 
     
     
       19. A method, as claimed in claim  14  wherein said knee frequency is about 300 MHz. 
     
     
       20. A method for source-terminating of a clock signal transmission line comprising: 
       series-connecting a resistance which has a value of about 750 ohms and a ferrite bead to provide a line termination component;  
       electrically coupling said termination component between said source and said transmission line; and  
       transmitting a sequential plural of clock signals from said source, along said transmission line.